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Atomic nucleus

An atom is made up of a tiny central region, the nucleus, containing all of the protons and neutrons of the atom. This means that the nucleus has a net positive charge.

The nucleus is surrounded by electron shells, which are orbits where electrons are found.

Electrons are kept in the electron shells by attractive forces between the positively charged protons and the negatively charged electrons.

Most of the mass of an atom (over 99.94%) is concentrated in the nucleus. The mass of an electron is negligible because its mass is $$\displaystyle{\frac{1}{1837}}$$ of a proton's.

The relative charges and masses of subatomic particles are obtained by dividing their individual charges/masses by the charge/mass of a proton.

The relative mass of a neutron is 1 as the mass of a proton is approximately equal to that of a neutron.

Summary of charges and masses of subatomic particles
Subatomic particle Relative charge Relative mass
Proton 1 1
Neutron 0 1
Electron $$-1$$ $$\displaystyle{\frac{1}{1837}}$$